Method of treating cellulose fibers



UNITED STATES F033 ligigmmg search PATENT OFFICE METHOD OF TREATING CELLULOSE FIBERS William Beach Pratt, Boston, Mass; Annette Harris Pratt, administratrix of said William Beach Pratt, deceased, assignor, by mcsne assignments, to Aldox Corporation, Dover, Del., a corporation of Delaware No Drawing. Application August 15, 1938, Serial No. 224,999. In Ganada August 28, 1937 4 Claims.

My invention relates to the treatment of natural vegetable cellulose fibers with aldehyde and oxidizing agents, particularly as a prelude to further processing, and my present application relates to the subject matter, and is in part a continuation of my applications Serial Nos. 31,443 filed July 15, 1935, 142,320 filed May 12, 1937, and 219,824 filed July 18, 1938. Serial No. 31,443 has now issued as Patent Number 2,126,809, patented August 16, 1938.

Cellulose vegetable fibers, such as cotton, flax, ramie, hemp and manila, consist primarily of cellulose, but contain in their natural or raw state certain non-cellulosic constituents of a gummy or waxy nature. I have found that the coloration of such natural fibers is largely or primarily due to the pigmentation'of the natural gums and waxes, which are removable by cold solvents therefor without staining the fiber. heating of the fibers in such solvents to a high temperature, say boiling, or the heating thereof in an aqueous alkaline solution, results in the staining of the cellulose of the fiber by the pigments contained in the gums or waxes, or by 25 some reaction product thereof. Kier-boiling fabrics composed of cellulose fibers containing heavily pigmented waxes, as, for instance, flax, in a hot alkaline bath imparts a deep staining to the cellulose of the fibers which is only removable with difiiculty, and is largely responsible for the long and severe bleaching to which such fabrics must ordinarily be subjected to whiten them.

I have discovered that the melting points of such waxes may be lowered and the pigments 35 rendered readily removable or bleachable, without staining the cellulose of the fiber, by subjecting the natural fiber, or yarns or fabrics composed thereof, to the action of an aqueous solution of formaldehyde at a temperature approximating 104 to 120 R, and then to the action of an oxidizing bleach, such, for instance, as hypochlorite. The duration of the treatment with the aqueous formaldehyde solution varies with the character of the fiber and with the character of the yarn or fabric in which it is embodied, but ordinarily a treatment for one-half hour will suiiice though a longer treatment is harmless to the fiber. When fibers so treated are subjected to the action of an aqueous hypochlorite solution of a strength and temperature usual for bleaching kier-boiled goods, the formaldehyde acts as a reducing agent on the oxidizingagent to liberate the oxygen and facilitate the desired bleach.

When goods composed of cotton fiber whose r waxy constituent contains little or no pigment are so treated, a considerable portion, roughly 50%, of the gums and waxes are removed therefrom, and the cellulose portions of the fibers and any pigment contained in the residual waxes are so bleached that the fabric is suitable for certain The uses without further extraction or bleaching, and the residual gums and waxes give weight and hand to the fabric. The fabrics so treated may, if desired, be further treated in accordance with my application Serial No. 142,320 to convert the cellulose of the fiber into cellulose hydrate; or they may be subjected to a mercerizing treatment, or to a usual kier-boil and bleaching treatment.

When my present invention is applied to the treatment of flax or other fibers containing heavily pigmented waxes or gums, the treated fabric may, (after complete removal of all free hypochlorite or reaction products of the bleach by usual methods of souring and washing) be kier-boiled in a hot alkaline bath without danger of staining the cellulose of the fibers by reaction products of the pigmented Waxes and alkali, and such kier-boiled goods may be then readily bleached in any usual manner.

I have discovered that for the successful treatment of cellulose fiber with formaldehyde in accordance with my invention, it is necessarythat the formaldehyde bath should be devoid of any free inorganic-acid or of substances (other than the constituents of the fiber) free to combine or condense with the formaldehyde. The presence of free inorganic acid in the bath, or heating the bath to boiling temperatures, results in such attachment of the formaldehyde to the cellulose that the formaldehyde is substantially irremovable therefrom by any oxidation which does not also degenerate the cellulose into oxycellulose. The presence in the bath of any substances, such as the alkalies or sodium bisulphite, which form condensation products with formaldehyde, or of substances free to combine with formaldehyde and having a greater affinity therefor than does cellulose, results in the production of reaction or condensation products which are condensed in or attached to the cellulose of the fiber and affect its physical or chemical characteristics. Such condensation and reaction products lack the reducing properties of formaldehyde per se and hence do notfacilitate the liberation of oxygen from the oxidizing agent contained in the bleaching bath to which the fabrics are subjected in accordance With my invention.

When, however, natural cellulose fibers are treated in a substantially neutral aqueous formaldehyde bath at a temperature approximating 104 to 120 F., the cellulose of the fiber is thoroughly impregnated with the formaldehyde. Such formaldehyde is, however, removable by thorough water washing. The formaldehyde treated fiber is introduced into the bleaching bath without washing out the formaldehydeand while the fiber is thoroughly impregnated therewith so that the ingress of the oxidizing bleach liquor into the fiber results in the liberation of oxygen in situ in the fiber by the reducing action of the formaldehyde.

To avoid the acidification of the bath of the small amount of formic acid contained in com mercial formalin, and also to avoid. introducing into the bath the coloring matter and resinous impurities contained in commercial formalin, I preferably volatilize the formaldehyde in the bath from trioxymethylene, the amount of trioxymethylene being preferably approximately 2% by weight based on the weight of the dry goods, though as little as one per cent may be used and an excess is not harmful. The treatments may be carried out in any suitable vessel, such as a dolly washer. Sufiicient water should be used. to thoroughly immerse and saturate the goods. The treatment may be carried out by repeated immersions of the goods and agitation thereof in thesame washer, in a batch operation, orthe treatment may be carried out in a range operation in which the goods are passed from one washer to another.

Various other oxidizing agents may be substituted for the hypochlorite, as for instance, so-

T dium perborate, hydrogen peroxide, or potassium permanganate. Where potassium permanganate is used as an oxidizing. agentthe goods should be washed and given a treatment in sodium acid sulphite to dissolve the brown manganese salts left in the goods.

The impregnation of the fibers with formaldehyde may also be effected by wetting the fibers with water and then exposing them to pure formaldehyde gas until a sufficient amount of gas has been absorbed by the moisture to thoroughly impregnate the fibers.

Not only are the cellulose and the wax of cotton fibers bleached and the wax rendered more readily removable by the described treatment with formaldehyde under conditions preventing the formation of extraneous condensation or reaction products, but the sheath or surface layer of the cell wall is densened and its characteristic gloss is preserved and intensified; Likewise the natural lustre and strength of bast fibers subjected to my treatment are maintained and augmented and the disintegration of bast fibers into individual cells is avoided. In fact bast fibers, after being subjected totreatment in accordance with my. invention, may be subjected to the action of caustic of mercerizing strength without deterioration of the fibers or of the bond between the cells thereof. By subjecting bast fibers. to caustic of mercerizing strength, with or without tension, the bast fiber yarn or fabric is given increased strength, lustre, absorption to dyestuffs and improved feel or handling.

Union fabrics, as for instance, fiat fabrics o01nposed of cotton and linen yarns or plushes having a cotton backing and animal fiber pile, may be advantageously treated with formaldehyde and an oxidizing agent under the conditions above specified. Where plush having a cotton backing and animal fiber pile is to be treated in accordance with, my invention, the animal fiber is preferably given a preliminary treatment with ammonia, which should be well washed out before the treatment with the formaldehyde. The pile of pile fabric so treated has unusual loftiness and freedom from matting of the fibers so that the requisite tigering and'finishing operations may be reduced.

While the formaldehyde solution should be substantially neutral and its temperature should not materially exceed F. when the bleaching of the waxes and cellulose and partial removal of such waxes is the primary objective of the treatment, the temperature may be raised considerably above this and the bath may have a pH value of nine-or higher when the primary objective of the treatment is the conversion of the cellulose into cellulose hydrate, as set out in my application Serial No. 142,320. Such treatments may be given separately, or may be given sequentially, or may be given as a part of the same operation by adding to the bleaching bath a neutral soap and borax and increasing the temperature thereof to, say, to F. Under such conditions, and provided the bath is kept devoid of substances free to combine or form condensation products with the formaldehyde, the formaldehyde becomes so firmly attached to the cellulose as to be irremovable therefrom by repeated water washing and so retains its aldehydic characteristic as to be capable of precipitating copper throughout the fiber from Fehling solution. Such formaldehyde is removable from the fiber in the presence of water by an oxidizing agent, such as hypochlorite, which is harmless to the fiber. Fiber so treated with aldehyde has distinctly different characteristics from cellulose treated with formaldehyde at high temperatures, viz., at or. above 0 boiling.

Having described my invention, I claim:

1. The method of treating natural cellulose fibers which comprises subjecting such fibers to an aqueous formaldehyde bath devoid of sub stances, other than the constituents of the fiber, free to combine or condense with the formaldehyde at a temperature and for a time sufficient to impregnate the fibers but insuflicient for an attachment of formaldehyde to the cellulose resistant to water washing, and then treating the impregnated fibers with an aqueous bath containing an oxidizing bleaching agent activated by the formaldehyde impregnating the fibers.

2. The method of treating vegetable fibers which comprises subjecting such fibers to the action of an aqueous formaldehyde bath at a temperature approximating 104 to 120 F., such bath being devoid of inorganic acids and also devoid of substances, other than the constituents of the fiber, free to combine or condense with the formaldehyde, and then treating the fiber in an aqueous bath containing an oxidizing bleaching agent activated by the formaldehyde for a time insuificient to oxidize the cellulose of the fiber.

3. The method of treating vegetable fibers containing natural waxes which comprises treating suchfibers with an aqueous solution of formaldehyde devoid of substances, other than the natural constituents of the fiber, free to combine or form condensation products with form fibers in an aqueous bath containing formaldehyde volatilized therein from trioxymethylene.

and devoid of acid and devoid of substances,

other than the fiber, free to combine or form condensation products with formaldehyde.

WILLIAM BEACH PRATT. 

